libobs/media-io: Increase TS smooth threshold to 70ms

With certain devices (AVerMedia C985 and LGP), audio timestamps are
bad, and a 50ms threshold of audio data "smoothing" (making consecutive
audio packets seamless with one another) isn't enough to handle bad
consecutive timestamp values.  After testing, 70ms sufficiently solves
the issue.

libobs/media-io/media-io-defs.h

@@ -21,4 +21,4 @@
 
 /* time threshold in nanoseconds to ensure audio timing is as seamless as
  * possible */
-#define TS_SMOOTHING_THRESHOLD 50000000ULL
+#define TS_SMOOTHING_THRESHOLD 70000000ULL